Adjustable boring bars employing an offset principal are known in the art usually employing an intermediate eccentric sleeve interposed between the boring bar and head of the tool with somewhat complex manufacturing provisions for achieving accuracy. Also a tool is disclosed in U.S. Pat. No. 2,643,556 wherein a conical offset socket seats a conically tapered boring bar which is clamped against rotation after adjustment under axial spring loading by a keyed split nut threaded on the inner end of the conical boring bar adapted to react against a plurality of springs seated in the socket.
Another example of the closest known prior art is an eccentrically mounted boring head disclosed in U.S. Pat. No. 2,931,254 wherein preloaded balls are employed to facilitate rotational adjustment under axial spring loaded frictional shoulder engagement relied upon for retaining the boring bar in adjusted position.
In U.S. Pat. No. 4,022,539 a discreet adjustment is achieved with interengaging splined elements retaining the boring bar in rotationally adjusted position.